This invention relates to radio control systems for the remote actuation of a load. More particularly, it involves a device for encoding and decoding digital electrical signals, with the decoder activating an external load if the received signal corresponds to a preselected code.
Remote actuation of garage door openers and similar loads have been accomplished traditionally by means of a radio control system wherein transmitters and receivers are matched to one another by frequency selection. An inherent disadvantage of this approach is the limited number of available carrier frequencies and the possibility of a match between transmitter and receiver belonging to different persons.
With an increasing awareness of such a potential security problem, the recent trend in providing remotely actuated garage door openers is to provide the owner with the capability of selecting his own personalized code in the transmitter and receiver sections. Many of the recent systems employ digital coding techniques in which the owner selects a particular combination of switches to set the code. Representative examples of known control systems are disclosed in U.S. Ser. No. 674,595, filed Apr. 7, 1976, now U.S. Pat. No. 4,141,010, issued Feb. 20, 1979 to Umpleby, and assigned to the assignee of the present invention; U.S. Pat. No. 3,906,348 to Wilmott; and U.S. Pat. No. 4,037,201 to Wilmott.
Although the commercially available remote control garage door openers have been gaining wide acceptance, they have been plagued with relatively high manufacturing costs. One of the most expensive items of such systems is the mounting of the various discrete electrical components of the circuitry onto printed circuit boards and the like. The number of discrete components that comprise the circuitry that must be manufactured and assembled bears heavily on the relationship to cost. Efforts have been made to minimize the number of components in such systems utilizing, for example, integrated circuit technology. However, the encoder-transmitter section and the decoder-receiver section have always been considered as separate entities. Consequently, each section was manufactured and designed separately utilizing different components to perform their intended functions. According to the broadest aspect of the present invention, it has been discovered that an encoder-decoder system can be designed having a majority of commonly used functional components. Accordingly, such a circuit can be readily implemented on an integrated circuit device which serves the dual purpose of both the encoding and decoding functions depending merely upon the external connections made to the device. The device of the present invention does not merely duplicate known discrete components into integrated circuit form on different parts of the chip, but utilizes the common functional portions in both modes of operation. Therefore, the cost of such systems can be drasticly reduced by minimizing the chip size and functional portions thereof, the number of external connections made to the device, and by permitting a common packaging scheme for both the encoder and decoder, thereby resulting in lower production costs by improving efficiency of operation.
The prior art has made several attempts to increase the security of remotely actuated control systems. Primarily, they have provided an increasing number of code selecting switches thereby increasing the number of permissible codes. It has also been suggested to delay the actuation of the load until a predetermined number of consecutive codes has been received. Unfortunately, the transmission of the encoded signals may often be in a relatively noisy electrical environment. Consequently, in such an environment, it is possible for an authorized user to be transmitting the correct code, but not be correctly received for the required number of consecutive times. The number of correct consecutive codes necessary to activate the load could be reduced, but only with the resultant decrease in security. In comparison, a feature of the present invention provides improved circuitry by which the security of the system is maintained yet accommodates an occasionally erroneous signal due to a noisy electrical environment. Still another feature of this invention gives the user the option of tailoring the tolerance level of the decoder section to determine the degree of correspondence between incoming signals and the comparison or local code that is internally generated by the decoder section. Accordingly, the user in an electrically noisy location is still able to use the system of the present invention by adjusting the tolerance level or degree of permissible error in the decoder.